Typical horizontal side-moving doors include either a rigid or semi-rigid planar door panel that translates horizontally in front of a doorway or a flexible door panel that coils about a roller as a leading edge of the flexible panel translates horizontally in front of the doorway. Horizontal side-moving doors with a flexible panel and a roller can be referred to as horizontal side-rolling doors.
Horizontal side-rolling doors, such as the one disclosed in U.S. Pat. No. 4,096,902, include one or two vertical rollers at either one or both lateral edges of the doorway. Some horizontal side-rolling doors have a single roller at one side of the doorway with a single curtain that extends and retracts across the full width of the doorway.
In some cases, the “single curtain” is actually comprised of two layers, each having its own vertical take-up roller. In such cases, the two rollers are right next to each other at one lateral edge of the doorway. As the door opens, the two layers of the curtain separate at the edge of the doorway and wrap upon their respective rollers.
Other horizontal side-rolling doors include two individual curtains, each supported by its own roller at opposite lateral edges of the doorway. For such doors, the leading edges of the two separate curtains meet at the center of the doorway as the door closes. To open the door, the two curtains move apart from each other and wrap upon their own roller (or set of rollers if each curtain has two layers).
The leading edges of side-rolling curtains and planar door panels are often reinforced by a relatively rigid, vertically elongate member that can be susceptible to being accidentally struck by a forklift passing through the doorway. To prevent permanent damage to the door in the event of a collision, the door panel or curtain is often made to restorably break away.